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Glomerular representation of plant volatiles and sex pheromone components in the antennal lobe of the female Spodoptera littoralis

Medhat M. Sadek¹, Bill S. Hansson^1,2, Jean Pierre Rospars³ and Sylvia Anton^1,2,*

¹ Division of Chemical Ecology, Department of Ecology, Lund University, SE-223 62 Lund, Sweden
² Division of Chemical Ecology, Department of Crop Science, Swedish University of Agricultural Sciences, PO Box 44, SE-230 53 Alnarp, Sweden
³ Unité de Biométrie and Unité de Phytopharmacie, Institut National de la Recherche Agronomique, F-78026 Versailles Cedex, France

View larger version (58K): [in a new window]   Fig. 1. Reconstructed glomerular structure (A-D) of the anterior aspect of the antennal lobe (AL) of the female S. littoralis moth and a typical optical section (E) of the AL. (A) Right and (B) left ALs of the same female, respectively; (C,D) the left ALs of two other different individuals. Landmark glomeruli (red) are denoted by the letters A-F. The other glomeruli are roughly divided into three groups (dark green, yellow and pink) and numbered to facilitate the use of the figure as a reference for the identification of glomeruli targeted by responding neurones (see the text). AN, antennal nerve; LC, lateral cell body cluster; MC, median cell body cluster. Scale bars, 100 µm.

View larger version (38K): [in a new window]   Fig. 2. Responses (action potentials) of a generalist neurone (number 92) to several compounds, indicating degrees of response and the various delays after the application of stimuli. Compounds are given in the order of their application. TMTDT is (E,E)-4,8,12- trimethyl-1,3,7,11-tridecatetraene. The thick horizontal bar indicates the time at which the compound was applied. 0, no response; +, a weak response; ++, an intermediate response; +++, a strong response (see Materials and methods for details).

View larger version (41K): [in a new window]   Fig. 5. (A) Morphology of neurobiotin-stained projection neurones (PNs) reconstructed from 10µm frontal sections. Arborisations within the antennal lobe are uniglomerular. The targeted glomerulus was identified (using the reference in Fig. 1) and indicated by the number alongside. Axons of both neurones leave the antennal lobe through the inner antennocerebral tract. Protocerebral projections arborise within the calyces of the mushroom body (CMB) and then supply the lateral protocerebrum (LP). Broken lines indicate the borders of the CMB. Scale bar, 100µm. (B) Responses of the generalist neurone (number 112) to repeated stimulation by two compounds. Other stimuli had been tested in between. The thick horizontal bar indicates the time at which the compound was applied.

View larger version (54K): [in a new window]   Fig. 4. (A) Morphology of the neurobiotin-filled local interneurones (LNs) reconstructed by projecting optical sections (2.5 µm thick) prepared using a confocal microscope. The two LNs were selected to show homogenous (number 97) and heterogeneous (number 98) branching patterns. Scale bar, 100 µm. (B) Typical response of a local interneurone to benzaldehyde and control (blank). The thick horizontal bar indicates the time at which the compound was applied.

View larger version (32K): [in a new window]   Fig. 3. (A) Degrees of specificity exhibited by the examined interneurones. (B) The percentage of responses obtained for various compounds in relation to the number of times the compound was applied. Recordings were made from 153 neurones.

View larger version (37K): [in a new window]   Fig. 6. Reconstructed antennal lobes indicating the glomerulus targeted by a specific projection neurone (PN). The three neurones arborised in the same glomerulus, C (blue). Although some glomeruli were not reconstructed in number 104, the targeted glomerulus was easily identifiable because it is one of the landmark glomeruli. For reference see Fig. 1. +++, strong response; ++, moderate response; +, weak response; 0, no response. Scale bar, 100 µm.

View larger version (44K): [in a new window]   Fig. 7. Reconstructed antennal lobes with two physiologically similar projection neurones (PNs) arborising in different, and distantly located, glomeruli (blue). The glomerulus innervated by neurone 108 is the landmark glomerulus E. Response profiles are given as in Fig. 6. Scale bar, 100 µm.

View larger version (37K): [in a new window]   Fig. 8 . Reconstructed antennal lobes with two physiologically non-overlapping types of neurones arborising in two different but adjacent glomeruli (blue). Response profiles are given as in Fig. 6. Scale bar, 100 µm.

View larger version (55K): [in a new window]   Fig. 9 . Representation of the ten tested odours in the AL glomeruli. Patterns are drawn based on the morphology of 19 stained projection neurones, where glomeruli targeted by responding neurones are blue. For glomeruli harbouring the dendritic arborisations of more than one neurone, the number of innervating neurones is given on the glomerulus. Numbers in the lower left-hand corners are the numbers of stained projection neurones for a given compound.